1. Field of the Invention
This invention relates to an electromagnetic reciprocating pump, and more particularly relates to an electromagnetic reciprocating pump which permits the amount of suction or discharge or the degree of vacuum or compression to be selected at multiple stages.
2. Description of the Prior Art
A fluidal machine such as the electromagnetic reciprocating pump or compressor is provided, as disclosed in the specification of Japanese Patent Publication SHO No. 57(1982)-30,984 or Japanese Utility Model Appln. SHO No. 59(1984)-141,664, for example, with a cylinder and a piston which jointly engage in transfer of a fluid and a magnetic armature which is integrally formed with the piston.
Around the magnetic armature is disposed a stationary electromagnet adapted to drive it. The stationary electromagnet, on application thereto of a half-wave alternating current or a pulse current, attracts the magnetic armature in the direction of axis and, on release of the applied current, allows the magnetic armature to be returned by the repulsive action of a return spring. Thus, the piston which is formed integrally with the magnetic armature is reciprocated to permit transfer of a fluid.
The number of reciprocation of the piston, therefore, equals the frequency of the half-wave alternating current applied to the stationary electromagnet. For the electromagnetic reciprocating pump to be driven with high efficiency, it is necessary that the frequency of the alternating current mentioned above should substantially agree with the natural frequency of the reciprocating system composed of the piston, the magnetic armature, and the return spring.
The prior art described above, has posed the following problem.
There is felt the need of enabling the electromagnetic reciprocating pump to vary the amount of suction or discharge or the degree of vacuum or compression. To realize this need, it is necessary that the frequency of the half-wave alternating current applied to the stationary electromagnet should be varied.
When the frequency of the half-wave alternating current applied to the stationary electromagnet does not agree with the natural frequency of the reciprocating system composed of the piston, the magnetic armature, and the return spring, the loss of energy is increased the electromagnetic reciprocating pump cannot be efficiently driven.